1. Field of the Invention
The present invention relates to a cell reselection method and apparatus for a packet data service in a mobile communication terminal. More particularly, the present invention relates to a method and an apparatus for reselecting a cell between an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) system and a non E-UTRAN system.
2. Description of the Related Art
Currently, three schemes including Global System for Mobile communication (GSM) system which is a second-generation system, and synchronous Code Division Multiple Access 2000 (CDMA2000) system and Universal Mobile Telecommunication Services (UMTS) system which are the third-generation systems are being used. The UMTS leads the standardization in the 3rd-Generation Partnership Project (3GPP). The UMTS system features efficient high-rate data/multimedia service up to 2 Mbps, which is a high data rate than the existing second-generation system. Standardization of Long Term Evolution (LTE) which is a fourth-generation system is currently being developed. The purpose of the LTE is to establish an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN).
A UMTS Terrestrial Radio Access Network (UTRAN) system and a GSM Enhanced Data Rates for Global Evolution (EDGE) Radio Access Network (GERAN) system presently support both a Circuit Switch (CS) scheme and a Packet Switch (PS) scheme, whereas the E-UTRAN system supports only the PS scheme. While the LTE supports a voice call based on Internet Protocol (IP) Multimedia Subsystem (IMS), most providers do not adopt the IMS and only few providers intend to adopt the IMS. Thus, the LTE standard suggests a CS fallback service to support the voice call.
When a mobile communication terminal supporting the LTE is camping in a cell of the E-UTRAN and a Mobile Originate (MO) call or a Mobile Terminate (MT) call takes place, the CS fallback service hands the mobile communication terminal to a non E-UTRAN and then processes the voice call.
Meanwhile, a current E-UTRAN system employs a priority based cell reselection scheme. A Release 7 version of the UMTS system of uses a best cell based cell reselection scheme. Accordingly, in an area covering both of the E-UTRAN system using the priority based reselection and the system using the best cell based cell reselection, the mobile communication terminal supporting the LTE may not normally use the packet service.
For example, when the mobile communication terminal supporting the LTE is using the packet service over the E-UTRAN and the MT call takes place, both of the CS call and the packet services are handed over to the non E-UTRAN to provide continuous service to a user. However, when the packet service cannot be handed over to the non E-UTRAN because of characteristics such as transfer rate or bandwidth, the E-UTRAN suspends the packet service and transmits a paging message indicating a Core Network (CN) domain field value with the CS to the mobile communication terminal. The mobile communication terminal receiving the paging message recognizes the CS call issued to itself, hands over to the cell of the UTRAN or the GERAN through the CS fallback procedure, and thus receives only the CS call service. Herein, when the CS call ends, the mobile communication terminal reselects the cell of the E-UTRAN to receive the suspended packet service. However, since the UTRAN or the GERAN is using the best cell based cell reselection scheme, when a cell signal of the UTRAN or the GERAN is good, the mobile communication terminal does not attempt the signal measurement for the cell reselection. As a result, the mobile communication terminal cannot receive the suspended packet service.
Therefore, a need exists for a cell reselection method and apparatus for receiving a packet served of the cell reselection.